First Canadian mixshield TBM completes Second Narrows Water Supply Tunnel

5 October 2021

Excavation has been completed on Metro Vancouver’s tunnel under the Burrard Inlet which will convey drinking water from the North Shore to households throughout the region.

The Second Narrows Water Supply Tunnel project is the first in Canada to have been excavated by a mixshield TBM and involves a 5.8m-diameter, segmentally-lined water supply tunnel 30m under Burrard Inlet. It is being constructed by Traylor-Aecon General Partnership, a consortium of Traylor Infrastructure Canada, and Aecon Infrastructure. McMillen Jacobs is engineer of record for all underground structures and prime consultant for the design team, which includes AECOM and Golder.

As one of five new regional water supply tunnels, the project is designed to meet current seismic standards to ensure continued water supply after a major earthquake. The tunnel will replace three existing water mains built in 1948, 1954 and 1978.

Launched in September 2020, the Herrenknecht 6.64m-diameter TBM Lynn-Marie is the first mixshield/slurry TBM to be used in Canada and was launched in the summer of 2020 from the 60m-deep, 16m-diameter shaft in North Vancouver on the north side of the inlet. The 1.1km-long tunnel alignment terminates in a 110m-deep, 10m-diameter shaft in the City of Burnaby. Three steel water mains will be installed in the tunnel.

The machine – which had to provide around 6.5bar of support pressure – has mined through three distinct geological zones: sand and silt mixtures; a soil-to-rock transition zone with cobbles and boulders; and mostly weak sandstone.

Construction is expected to be completed in 2025.